The term "ergonomic armchair" generally refers to those pieces of seating furniture offering outstanding anatomical support and further allowing easy anatomical modification and repositioning, in accordance with the movements and wishes of the user.
More specifically, the armchair of this invention is of the type comprising a seating device, a supporting structure upon which the seating device is fitted, and a mechanism for joining the seating device and the seating structure and allowing regulation of the angular position of the seating device relative to the supporting element. The seating device may comprise a front cushioned element and a rear frame which is anchored to the regulating mechanism through the seating area and which is molded so that it has flexible cross-sectional fibs.
The position and anatomical modifications of the seating and seat back surfaces are generally achieved by combining the partial deformation capacity of the body defining the armchair seat and seat back areas with the action of a regulating mechanism that links the seating area to the lower supporting element.
European Patent No. 309,368 describes an armchair in which the frame of the seating device is made of only one piece and has cross-sectional deformation capacity. The mechanism that regulates the angular position of the seating device has a turning plate fitted upon a cross-sectional axis of the seating area and a spring disposed between a fixed point of the rigid support and the turning plate, so that whenever the seat tilts backwards, the plate turns and compresses the spring.
A proper seating device stability is not achieved for the seating device, in the various adjustable angular positions, unless the degree of compression of the spring is properly set beforehand as a function of the weight of the user. The seating device frame also requires a special arrangement to allow the upper portion of the seat back to bend backwards. The bending area of the upper seat back frame includes a structure built with flexible cross-sectional ribs that act as intermediate hinges. The seating frame has a structure formed on the basis of tubular profiles that run, upon the seating area, under that same area and within the seat back area.
The structure of such a seat back upper bending area increases fabrication costs considerably and does not allow a seat back high enough to support the shoulders, so that it does not offer maximum support, particularly for full back support. The structure does not permit transfer upon the seat certain torsion movements and furthermore does not support high seat back cross-sectional torsion movements. With respect to the seating area, the frame works under traction and flexion, thus reducing its working life.
European patents Nos. 309,368 and 309,369 describe a chair or armchair that includes a seating device made up by a back shell or frame and a front cushioned element. The back shell or frame, made of a plastic material piece, has a substantially rigid structure, except at an intermediate area of the seat back, which is flexible and deformable only in its longitudinal direction. This flexibility is achieved through a structure, in the intermediate seat back area, having parallel rigid cross-sectional blocks, consecutively connected by intermediate membranes with a greater flexibility. The capacity of deformation of the structure depends on the number of blocks and membranes, as well as of the width and nature of the membranes. The shell or frame includes a metal structure that extends below the back portion of the seating element, crosses the shell and extends above the flexible intermediate surface of the seat back.
This solution presents the problem that seat back deformation may extend beyond the limits desired if a relatively high force is applied against it.
The structure of the shell or frame also makes it considerably more expensive to manufacture and requires the use of materials capable of withstanding high deformation cycles, as it may otherwise result in the early breakage of some of the membranes forming part of the structure.
The only function of the metal structure of the frame is to lend it rigidity and, since it is disposed through the frame, it requires a complex assembly process.